1. Field of the Invention
The present invention relates to filing books with bag sheets. More particularly, the present invention relates to filing books with bag sheets which have a cover sheet with excellent stiffness and smoothness and can be prepared easily.
2. Description of the Prior Art
Filing books with bag sheets in which a number of plastic bag sheets are bound together to a form of book are widely used as filing books to keep documents, samples and the like.
There are three kinds of structures in the filing book with bag sheets. One has openings at the upper side of the book (upper opening). A second one has openings at the sides facing a folding part at a central part of the book (inside opening) and a third one has openings at both of opposite sides to the folding part of the book (outside opening). The structure of the inside opening is most widely used because this structure has less danger of losing the contents from the book.
Filing books with bag sheets entirely made of plastics are widely used. When these books are composed of bag sheets made of a thermoplastic film and a cover sheet also made of a thermoplastic film, the bag sheets can be fixed together with the cover sheet by heat sealing at the central part to the form of a book and fabrication of filing books can be performed easily.
Thus, it is necessary for the efficient fabrication of filing books in conventional practices that both of the cover sheet and the bag sheets are made of thermoplastic materials.
However, when cover sheets at the both sides of the front cover and the back cover of the book are made of plastic materials, filing books do not stand by themselves because of insufficient stiffness. This makes it difficult to store these filing books by standing them upright on desks, shelves and the like. Moreover, when a number of filing books are arranged in a row for storage, covering sheets of adjacent books do not move smoothly because they stick to each other. This creates another problem for storing filing books, particularly when the books are stored by standing in a row on desks, shelves and the like. The cover sheets of plastic creates still another problem in that the feeling to hands during the handling is rather uncomfortable and people do not like it.